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12-01-2009, 12:05 AM   #1
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## some electrical math need help

Ok I wanted to see what my load was with the A/C, oven, and dryer
on all at the same time.
I came across this site http://michaelbluejay.com/electricity/measure.html

After doing the bottom one for the analog meter I ended up with
one full rotation in 2 seconds after the math I ended up with 12,960.

Does this look right? Is it saying that its 13Kwh? And looking at the static number they have "3600" where did that number come from?

12-01-2009, 04:56 AM   #2
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Ok after looking at more web pages im guessing the 3600 is in seconds

So with said appliances running at the same time plus other things
I'm looking at about an average 54 amps @ 240v at any one given time?

 12-01-2009, 08:59 AM #3 Member   Join Date: Nov 2007 Location: Nashua, NH, USA Posts: 7,906 Rewards Points: 1,418 For the large items (oven, etc.) you named, the numbers look appropriate. At that moment the three items (and perhaps some lights or TV or other things also turned on) were together drawing about 54 amps at 240 volts or 13 kilowatts. If this load went on, constant, for an hour you will have consumed 13 kilowatt hours. If there were some 120 volt items turned on, chances are the current on one side of the 240 volt service won't be exactly the current on the other side, for example you might have 55 amps at 120 volts on one side and 53 amps at 120 volts on the other side, still a total of around 13 kw. (You could also say the latter as 53 volts at 240 volts across both sides plus 2 amps at 120 volts across one side.) __________________ The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit. Last edited by AllanJ; 12-01-2009 at 09:05 AM.
 12-01-2009, 12:05 PM #4 Member   Join Date: Jul 2008 Location: NW of D.C. Posts: 5,990 Rewards Points: 2,000
 12-01-2009, 07:27 PM #5 Newbie   Join Date: Jun 2009 Location: AZ Posts: 23 Rewards Points: 10 Thanks for the help, So if I was to get a backup gen what this tells me is I need at least 54 amp one to run what was running when I took the measurement correct?
 12-01-2009, 07:50 PM #6 Member   Join Date: Jan 2009 Location: South of Boston, MA Posts: 17,248 Rewards Points: 2,000 I'd never run the stove & dryer at the same time with power out Who dries clothes while the power is out ? And if the power was out I'd use fans instead of an AC Depends upon how you connect the Gen & local codes Some require an automatic gen to be able to handle the whole house load The more amps you need, the higher the cost Extended outage: You'd cook food, run the AC then while you eat Turn AC off, Do wash & dry - then turn AC back on I have a 6500w unit = ~28a @ 240v If I lose power all I really want to do is power my fridge, freezer, few lights & my pump for my hot water heating system You'd need a 13 kw unit at a bare Min - pretty big & expensive
 12-01-2009, 08:36 PM #7 Member   Join Date: Sep 2008 Location: Oregon Posts: 1,497 Rewards Points: 500 All the generators I've seen are rated in watts. (Or kW for thousand watts.) Here is a ballpark page to add up all the watts of everything you would want to have on at the same time. You can also look at the labels (nameplate) in what you have and correct the listed wattage with what you really have... http://www.consumerreports.org/cro/r...lclulator.html For example I have a 1000 watt microwave. My refrigerator has a label inside which says 8.5 amps. So I can go to the following link and convert that to watts with the calculator under "single phase" and use 120 for the voltage... http://www.jobsite-generators.com/po...lculators.html Then the next link discusses "start-up wattage" of things with electric motors in them and the reason to get a larger rated generator than the wattage listed on the appliances... http://www.lowes.com/lowes/lkn?actio...Generator.html Some generators are "electronics friendly" and produce "clean" electricity... First: Poor quality electricity from generators, etc... http://www.jkovach.net/projects/powerquality/ Next: "Electronics Friendly" generator search... http://www.google.com/search?hl=en&s...h&aq=f&oq=&aqi=
 12-01-2009, 08:57 PM #8 Member   Join Date: Sep 2008 Location: Oregon Posts: 1,497 Rewards Points: 500 Also new "portable" generators come with a GFCI outlet and this is not compatible with home electric wiring when a transfer switch is installed. You would need a special transfer switch to also switch the "neutral". The following product bulletin from a generator manufacturer recommends modifying the grounding on the generator to solve this problem... (But the generator would no longer be OSHA compliant.) http://www.gen-tran.com/assets/pdfs/...Bulletin20.pdf Neutral switching transfer switch example... http://www.briggsandstratton.com/pdf...m-Domestic.pdf
 12-01-2009, 11:38 PM #9 Licensed Electrician     Join Date: Jan 2009 Location: Rahway, NJ Posts: 168 Rewards Points: 150 The nameplate ratings on these appliances need to be known to come up with an accurate load calculation, especially for that A/C condensing unit because that's an inductive load and draws more power at start up than it does once it gets going. __________________ Union County, NJ, Licensed Electrician Classic Electric, LLC, Rahway, New Jersey
12-02-2009, 03:48 PM   #10
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Thank you all for the help least now it gets me on the right path.

Much appreciated.

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